The present invention relates to a device for measuring the neutron dose equivalent in stray radiation fields by means of neutron detectors and a moderator sphere in the center of which there is disposed one of the detectors for detecting thermal neutrons.
In the field of radiation protection monitoring there exists the task of measuring the dose equivalent of neutrons in stray neutron radiation fields. Devices for measuring the dose equivalent preferably comprise a spherical polyethylene moderator having a diameter of 30 to 16 cm, in the center of which there is disposed a thermal neutron detector, e.g. a BF.sub.3 counting tube, an LiI scintillation counter or a .sup.3 He counting tube. The indication of the neutron dose equivalent is independent of energy in a first approximation within the energy range of thermal neutrons up to 20 MeV. The response of an dose equivalent meter, however, is greater by up to a factor of 4 or 8, respectively, in the energy range of intermediate neutrons compared to a response in connection with fast neutrons (Alberts, W. G. et al, "European Workshop on Neutron Dosimetry for Radiation Protection" Physikalisch-Technische Bundesanstalt, Report ND-17, Braunschweig 1979).
In order to estimate the neutron dose equivalent more independent of the neutron energy spectroscopic measuring methods also are applied which employ .sup.3 He or recoil counters or a number of 7 to 15 polyethylene spheres having different diameters (multisphere measuring technique). An accurate determination of the neutron dose equivalent results from multiplication of the neutron fluence in a partial energy range with the respective neutron fluence-to-dose equivalent conversion factor. See, for example, Sanna, R. S. et al, "Neutron Measurements Inside PWR Containments", Environmental Measurements Laboratory, U.S. Department of Energy, Report EML-379, 1980. These methods, however, are very complicated and cannot be used routinely for measuring the neutron dose at reactors or accelerators.